Audi A4 B7 1.9 TDI: Won't Start? Troubleshooting

Dear diesel mechanics,

My A4 is having problems again.


In January 2017, it wouldn't start either. Back then, I turned the key, it ran for a short time (a few rotations) and then immediately shut off. The roadside assistance service helped me with starting spray. After about 10 seconds of cranking, it started with the spray.


Yesterday (one year later), this problem occurred again, after about 10 hours of inactivity. I then tried to warm up the engine using the auxiliary heater, but that didn't help. The starter had no trouble turning the engine over, but it simply wouldn't start.
The roadside assistance service then sprayed starting fluid into the air filter box again, after which the engine ran smoothly after about 3 seconds.


This morning, I decided to listen carefully in case it doesn't start again. Also, I preheated the engine with the auxiliary heater before starting it.
Turned the ignition on, the preheating light illuminated briefly. It started immediately, ran smoothly for about a second, and then turned off.
I then sprayed some starting fluid into the air filter box and turned the key as quickly as possible. It took a little longer to start (about 15 seconds of cranking), but then it finally started.

During these 15 seconds, I read out some values using VCDS (snapshot).
- Motor speed: 252 rpm.
- Injection volume: 41.7 mg/H.
- Air mass: 420.0 mg/H

The temperature sensors are providing reasonable values. The fuel pump in the tank is running and sounds normal.
Otherwise, the engine starts perfectly fine.

So, I guess he's trying to inject fuel, but it's not working. Am I right about that?
Where could the troubleshooting be continued? Should transparent fuel hoses be used to identify air bubbles?

If there is air in the fuel, there are several possibilities:
- Leak in or around the PD elements.
- Crack in the cylinder head.
- Leak in tandem pump / Tandem pump seal.
- Leak in pipes / at connections.
- Fuel filter

Does anyone have experience and can suggest where to start looking for leaks?

Hello,
I would first try to help by jump-starting the engine with jumper cables. The starting speed of 252 RPM seems a bit too low. There are engine control units that only release fuel at approximately 300 RPM.

Best regards,
Thilo.

Is the pre-pump running?

Hello klahaui, since the engine ran for a short time, I assume the starter is okay. According to the diagnostic values, the PD elements are also being activated.

Hi Rüdi, the pre-lift pump, if that's the one in the tank, is running normally, at least audibly.

Thank you very much!

Hello,

The starting speed of 252 rpm is too low!

Otherwise, as already correctly identified:

Quote:

If there is air in the fuel, there are several possibilities: - Leak in or around the PD elements. - Crack in the cylinder head. - Leak in tandem pump / Tandem pump seal. - Leak in pipes / at connections. - Fuel filter

Best regards, Rainer.